The present invention relates to a semiconductor device and method of making the semiconductor device.
In the conventional semiconductor devices, generally, a semiconductor chip is bonded onto a printed board (substrate) through an adhesive. A circuit pattern formed on the board is wire-bonded to the electrodes of the semiconductor chip. The semiconductor chip is sealed by a thermoplastic resin such as epoxy resin.
For the purpose of enabling the backside of the semiconductor chip to use as a ground potential or causing the heat from the semiconductor chip to dissipate in an efficient manner, there is a semiconductor device in which the semiconductor chip is fixedly mounted on a die pad formed by a copper foil superior both in electrical and thermal conductivities.
However, as an adhesive, such a semiconductor device uses a conductive paste comprising an epoxy resin and a filler of powdered silver added thereto. Since adhesion of the conductive paste is inferior to that of an insulative paste, the former cannot provide a sufficient adhesion. Thus, the semiconductor chip may undesirably be separated from the die pad.
Recently, there has been developed a semiconductor device comprising a package board of copper plate on which a semiconductor chip is fixedly mounted in order to improve the thermal dissipation, because the amount of heat generated by the semiconductor chip has been increased due to the increased processing speed and density in the semiconductor device.
In such a semiconductor device, the semiconductor chip is adhered directly to the copper plate. Thus, the semiconductor chip may be separated from the copper plate due to the difference in thermal expansion coefficient between the semiconductor chip and the copper plate, as in the reflow to the printed board of an electronic device. More particularly, the coefficient of linear expansion in the silicon forming the semiconductor chip is about 2.4xc3x9710xe2x88x926/deg. while that of the copper is about 1.7xc3x9710xe2x88x925/deg., resulting in one-digit difference therebetween. Therefore, a remarkably large difference of thermal deformation (or thermal expansion) will be produced between the semiconductor chip and the copper plate due to an increased heat in the reflow. This will causes a large thermal stress to act on the adhesive, leading to separation of the semiconductor chip.
Thus, the conventional semiconductor devices raised a problem with respect to the adhesive property between the semiconductor chip and the substrate.
To overcome such a problem in the prior art, an object of the present invention is to provide a semiconductor device which can improve the adhesion between the semiconductor chip and the substrate and a method of making such a semiconductor device.
(1) A semiconductor device according to the present invention comprises a semiconductor chip, a metallic portion on which the semiconductor chip is fixedly mounted and supported through an adhesive layer, the adhesive layer including a plurality of electrically conductive adhesive regions and a plurality of insulative adhesive regions together, and a resin for sealing the metallic portion and semiconductor chip.
The electrically conductive and insulative adhesive regions can easily be formed by electrically conductive and insulative adhesives arranged in an alternate and matrix pattern. The ratio of the electrically conductive adhesive regions to the insulative adhesive regions may be about 1:1.
According to the semiconductor device of the present invention which includes the conductive and insulative adhesive regions together, the semiconductor chip can firmly be fixed to the metallic portion by the insulative adhesive regions while at the same time the semiconductor chip can electrically be connected to the metallic portion by the conductive adhesive regions. In addition, the conductive adhesive can provide a superior heat dissipation since it contains as a filler a metal such as silver which is superior in thermal conductivity and thus can rapidly transmit the heat from the semiconductor chip to the metallic portion through the conductive adhesive regions. When the conductive and insulative adhesive regions are alternately arranged in a matrix pattern, the entire semiconductor chip can uniformly dissipate the heat and also provide a uniformly strong adhesion over the whole area. This can prevent an accident such as partial separation of the semiconductor chip from the metallic portion or other accident. When the proportion of the electrically conductive adhesive regions to the insulative adhesive regions is set to be about 1:1, a large adhesion can be provided with sufficient electrical and thermal conductivities.
(2) The semiconductor device of the present invention comprises a semiconductor chip, and a package board on which the semiconductor chip is fixedly mounted, the package board being formed of a metal plate, and the semiconductor chip being fixedly mounted on the metal plate through a thermal stress relaxation layer. The thermal stress relaxation layer may be an insulation film on which a wiring pattern is formed, or a resin such as a solder resist film. The metal plate may be phosphor deoxidized copper superior in electrical and thermal conductivities, such as C1220-(xc2xd) H or C1220-H defined by JIS.
Since in the semiconductor device of the present invention, the semiconductor chip is adhered to the metal plate which is the package board through the thermal stress relaxation layer, the thermal stress acting on the adhesive layer due to the difference in thermal expansion coefficient between the semiconductor chip and the metal plate can be absorbed and relaxed by the thermal stress relaxation layer. Thus, the semiconductor chip can be prevented from being separated from the metal plate under destroy of the adhesive layer. Since the metal plate is formed of more rigid phosphor deoxidized copper defined as C1220-(xc2xd)H or C1220-H by JIS, the metal (copper) plate can be made thinner than the prior art. Thus, the semiconductor device can be made thinner.
(3) The semiconductor device of the present invention comprises a semiconductor chip, a metallic package board on which the semiconductor chip is fixedly mounted, and an insulating film formed between the semiconductor chip and the package board. Each of the package board and insulating film. has at least one hole at part of an area fixed to the semiconductor chip. The hole may be sized such that an opened end thereof is fixedly mounted only on an outer periphery of the semiconductor chip. The semiconductor device may further comprise a radiator fixedly mounted on the semiconductor chip inside the hole and without contact to the opened end of the hole. The package board may have a coefficient of thermal expansion lower than that of the radiator, and the radiator may have a thermal conductivity higher than that of the package board. For example, the package board may be formed of iron and the radiator may be formed of copper.
Since the semiconductor device of the present invention has holes formed in the package board and insulating film, the area to be fixed to the semiconductor chip is reduced. Thus, a stress resulting from the difference in thermal expansion coefficient between the package board and the semiconductor chip is less transmitted to the semiconductor chip. In addition, the semiconductor chip can be prevented from being separated from the package board or being cracked. It is more effective that these holes are enlarged to secure the package board only to the outer periphery of the semiconductor chip. In such a case, any increased stress will not be produced since the radiator is smaller than the semiconductor chip even if the radiator is fixedly mounted in the holes. Generally, a material of higher thermal conductivity is also higher in coefficient of thermal expansion. However, the radiator fixedly mounted in the holes may be formed by any other suitable material. Particularly, if the radiator is formed of a material having its thermal conductivity higher than that of the package board, the stress is reduced while at the same time the heat radiation is increased. For example, the package board may be formed of iron and the radiator may be formed of copper.
(4) The semiconductor device of the present invention comprises a semiconductor chip, a metallic package board on which the semiconductor chip is fixedly mounted, and a sealing portion for sealing the semiconductor chip, the semiconductor chip being fixedly mounted on the package board through the same material as that of the sealing portion.
In the semiconductor chip of the present invention, the member fixedly connecting the package board to the semiconductor chip is formed of the same material as that of the sealing portion for sealing the semiconductor chip. More particularly, the semiconductor chip is covered with the material forming the sealing portion, including the interface between the semiconductor chip and the package board. Thus, the stress from the package board is dispersed also to the member forming the sealing portion. Therefore, the stress exerted to the semiconductor chip is relaxed. This prevents the semiconductor chip from being separated from the package board or being cracked.
(5) The semiconductor device of the present invention comprises a semiconductor chip, a first metallic package board on which the semiconductor chip is fixedly mounted, and a second metallic package board having an opening. The semiconductor chip is positioned in the opening of the second package board, and the second package board has its thermal conductivity higher than that of the first package board. The first package board has its thermal expansion coefficient lower than that of the second package board and is fixedly mounted on an edge of the opening in the second package board through a thermally conductive adhesive member. For example, the first package board may be formed of iron and the second package board may be formed of copper.
Since in the semiconductor device of the present invention, the first package board on which the semiconductor chip is fixedly mounted has its thermal expansion coefficient lower than that of the second package board, the stress exerted to the semiconductor chip is reduced. The heat radiation is improved since the second package board has its thermal conductivity higher than that of the first package board. Such a design may be provided by the fact that the first package board is formed of iron and the second package board is formed of copper.
(6) The present invention further provides a method of making the aforementioned semiconductor device, comprising a step of fixedly mounting a semiconductor chip on a metallic portion through an adhesive, such a step further comprising steps of simultaneously injecting an electrically conductive adhesive and an insulative adhesive onto the metallic portion through a plurality of nozzles and curing the adhesives while they are brought into contact with the semiconductor chip. The nozzles for injecting the electrically conductive and insulative adhesives may alternately be arranged in a matrix pattern.
In this method, the conductive and insulative adhesive regions can simultaneously be arranged over the metallic portion by injecting the conductive and insulative adhesives through the multiple nozzles. This can be performed by a single step, resulting in reduction of the manufacturing cost.